Abstract: A wiring substrate connects an electrical system of a towed vehicle to an electrical system of a towing vehicle and includes a wiring connector configured to connect to a connector from a wiring harness of the towed vehicle, a first set of connections to connect to tail light assemblies in the towed vehicles, a second set of connections to connect to vehicle signal connections in the towed vehicle, the first and second sets of connections electrically coupled on the wiring substrate by at least one diode, and a third set of connections to connect to the towing vehicle.